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282 lines
12 KiB
Plaintext
282 lines
12 KiB
Plaintext
Filename: 135-private-tor-networks.txt
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Title: Simplify Configuration of Private Tor Networks
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Author: Karsten Loesing
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Created: 29-Apr-2008
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Status: Closed
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Target: 0.2.1.x
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Implemented-In: 0.2.1.2-alpha
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Change history:
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29-Apr-2008 Initial proposal for or-dev
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19-May-2008 Included changes based on comments by Nick to or-dev and
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added a section for test cases.
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18-Jun-2008 Changed testing-network-only configuration option names.
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Overview:
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Configuring a private Tor network has become a time-consuming and
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error-prone task with the introduction of the v3 directory protocol. In
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addition to that, operators of private Tor networks need to set an
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increasing number of non-trivial configuration options, and it is hard
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to keep FAQ entries describing this task up-to-date. In this proposal we
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(1) suggest to (optionally) accelerate timing of the v3 directory voting
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process and (2) introduce an umbrella config option specifically aimed at
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creating private Tor networks.
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Design:
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1. Accelerate Timing of v3 Directory Voting Process
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Tor has reasonable defaults for setting up a large, Internet-scale
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network with comparably high latencies and possibly wrong server clocks.
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However, those defaults are bad when it comes to quickly setting up a
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private Tor network for testing, either on a single node or LAN (things
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might be different when creating a test network on PlanetLab or
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something). Some time constraints should be made configurable for private
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networks. The general idea is to accelerate everything that has to do
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with propagation of directory information, but nothing else, so that a
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private network is available as soon as possible. (As a possible
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safeguard, changing these configuration values could be made dependent on
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the umbrella configuration option introduced in 2.)
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1.1. Initial Voting Schedule
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When a v3 directory does not know any consensus, it assumes an initial,
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hard-coded VotingInterval of 30 minutes, VoteDelay of 5 minutes, and
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DistDelay of 5 minutes. This is important for multiple, simultaneously
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restarted directory authorities to meet at a common time and create an
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initial consensus. Unfortunately, this means that it may take up to half
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an hour (or even more) for a private Tor network to bootstrap.
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We propose to make these three time constants configurable (note that
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V3AuthVotingInterval, V3AuthVoteDelay, and V3AuthDistDelay do not have an
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effect on the _initial_ voting schedule, but only on the schedule that a
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directory authority votes for). This can be achieved by introducing three
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new configuration options: TestingV3AuthInitialVotingInterval,
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TestingV3AuthInitialVoteDelay, and TestingV3AuthInitialDistDelay.
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As first safeguards, Tor should only accept configuration values for
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TestingV3AuthInitialVotingInterval that divide evenly into the default
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value of 30 minutes. The effect is that even if people misconfigured
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their directory authorities, they would meet at the default values at the
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latest. The second safeguard is to allow configuration only when the
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umbrella configuration option TestingTorNetwork is set.
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1.2. Immediately Provide Reachability Information (Running flag)
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The default behavior of a directory authority is to provide the Running
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flag only after the authority is available for at least 30 minutes. The
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rationale is that before that time, an authority simply cannot deliver
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useful information about other running nodes. But for private Tor
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networks this may be different. This is currently implemented in the code
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as:
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/** If we've been around for less than this amount of time, our
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* reachability information is not accurate. */
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#define DIRSERV_TIME_TO_GET_REACHABILITY_INFO (30*60)
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There should be another configuration option
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TestingAuthDirTimeToLearnReachability with a default value of 30 minutes
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that can be changed when running testing Tor networks, e.g. to 0 minutes.
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The configuration value would simply replace the quoted constant. Again,
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changing this option could be safeguarded by requiring the umbrella
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configuration option TestingTorNetwork to be set.
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1.3. Reduce Estimated Descriptor Propagation Time
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Tor currently assumes that it takes up to 10 minutes until router
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descriptors are propagated from the authorities to directory caches.
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This is not very useful for private Tor networks, and we want to be able
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to reduce this time, so that clients can download router descriptors in a
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timely manner.
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/** Clients don't download any descriptor this recent, since it will
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* probably not have propagated to enough caches. */
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#define ESTIMATED_PROPAGATION_TIME (10*60)
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We suggest to introduce a new config option
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TestingEstimatedDescriptorPropagationTime which defaults to 10 minutes,
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but that can be set to any lower non-negative value, e.g. 0 minutes. The
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same safeguards as in 1.2 could be used here, too.
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2. Umbrella Option for Setting Up Private Tor Networks
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Setting up a private Tor network requires a number of specific settings
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that are not required or useful when running Tor in the public Tor
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network. Instead of writing down these options in a FAQ entry, there
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should be a single configuration option, e.g. TestingTorNetwork, that
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changes all required settings at once. Newer Tor versions would keep the
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set of configuration options up-to-date. It should still remain possible
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to manually overwrite the settings that the umbrella configuration option
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affects.
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The following configuration options are set by TestingTorNetwork:
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- ServerDNSAllowBrokenResolvConf 1
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Ignore the situation that private relays are not aware of any name
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servers.
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- DirAllowPrivateAddresses 1
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Allow router descriptors containing private IP addresses.
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- EnforceDistinctSubnets 0
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Permit building circuits with relays in the same subnet.
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- AssumeReachable 1
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Omit self-testing for reachability.
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- AuthDirMaxServersPerAddr 0
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- AuthDirMaxServersPerAuthAddr 0
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Permit an unlimited number of nodes on the same IP address.
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- ClientDNSRejectInternalAddresses 0
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Believe in DNS responses resolving to private IP addresses.
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- ExitPolicyRejectPrivate 0
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Allow exiting to private IP addresses. (This one is a matter of
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taste---it might be dangerous to make this a default in a private
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network, although people setting up private Tor networks should know
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what they are doing.)
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- V3AuthVotingInterval 5 minutes
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- V3AuthVoteDelay 20 seconds
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- V3AuthDistDelay 20 seconds
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Accelerate voting schedule after first consensus has been reached.
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- TestingV3AuthInitialVotingInterval 5 minutes
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- TestingV3AuthInitialVoteDelay 20 seconds
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- TestingV3AuthInitialDistDelay 20 seconds
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Accelerate initial voting schedule until first consensus is reached.
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- TestingAuthDirTimeToLearnReachability 0 minutes
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Consider routers as Running from the start of running an authority.
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- TestingEstimatedDescriptorPropagationTime 0 minutes
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Clients try downloading router descriptors from directory caches,
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even when they are not 10 minutes old.
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In addition to changing the defaults for these configuration options,
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TestingTorNetwork can only be set when a user has manually configured
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DirServer lines.
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Test:
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The implementation of this proposal must pass the following tests:
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1. Set TestingTorNetwork and see if dependent configuration options are
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correctly changed.
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tor DataDirectory . ControlPort 9051 TestingTorNetwork 1 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000"
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telnet 127.0.0.1 9051
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AUTHENTICATE
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GETCONF TestingTorNetwork TestingAuthDirTimeToLearnReachability
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250-TestingTorNetwork=1
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250 TestingAuthDirTimeToLearnReachability=0
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QUIT
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2. Set TestingTorNetwork and a dependent configuration value to see if
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the provided value is used for the dependent option.
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tor DataDirectory . ControlPort 9051 TestingTorNetwork 1 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000" \
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TestingAuthDirTimeToLearnReachability 5
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telnet 127.0.0.1 9051
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AUTHENTICATE
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GETCONF TestingTorNetwork TestingAuthDirTimeToLearnReachability
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250-TestingTorNetwork=1
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250 TestingAuthDirTimeToLearnReachability=5
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QUIT
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3. Start with TestingTorNetwork set and change a dependent configuration
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option later on.
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tor DataDirectory . ControlPort 9051 TestingTorNetwork 1 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000"
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telnet 127.0.0.1 9051
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AUTHENTICATE
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SETCONF TestingAuthDirTimeToLearnReachability=5
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GETCONF TestingAuthDirTimeToLearnReachability
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250 TestingAuthDirTimeToLearnReachability=5
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QUIT
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4. Start with TestingTorNetwork set and a dependent configuration value,
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and reset that dependent configuration value. The result should be
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the testing-network specific default value.
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tor DataDirectory . ControlPort 9051 TestingTorNetwork 1 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000" \
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TestingAuthDirTimeToLearnReachability 5
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telnet 127.0.0.1 9051
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AUTHENTICATE
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GETCONF TestingAuthDirTimeToLearnReachability
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250 TestingAuthDirTimeToLearnReachability=5
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RESETCONF TestingAuthDirTimeToLearnReachability
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GETCONF TestingAuthDirTimeToLearnReachability
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250 TestingAuthDirTimeToLearnReachability=0
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QUIT
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5. Leave TestingTorNetwork unset and check if dependent configuration
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options are left unchanged.
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tor DataDirectory . ControlPort 9051 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000"
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telnet 127.0.0.1 9051
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AUTHENTICATE
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GETCONF TestingTorNetwork TestingAuthDirTimeToLearnReachability
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250-TestingTorNetwork=0
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250 TestingAuthDirTimeToLearnReachability=1800
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QUIT
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6. Leave TestingTorNetwork unset, but set dependent configuration option
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which should fail.
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tor DataDirectory . ControlPort 9051 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000" \
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TestingAuthDirTimeToLearnReachability 0
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[warn] Failed to parse/validate config:
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TestingAuthDirTimeToLearnReachability may only be changed in testing
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Tor networks!
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7. Start with TestingTorNetwork unset and change dependent configuration
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option later on which should fail.
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tor DataDirectory . ControlPort 9051 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000"
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telnet 127.0.0.1 9051
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AUTHENTICATE
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SETCONF TestingAuthDirTimeToLearnReachability=0
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513 Unacceptable option value: TestingAuthDirTimeToLearnReachability
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may only be changed in testing Tor networks!
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8. Start with TestingTorNetwork unset and set it later on which should
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fail.
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tor DataDirectory . ControlPort 9051 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000"
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telnet 127.0.0.1 9051
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AUTHENTICATE
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SETCONF TestingTorNetwork=1
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553 Transition not allowed: While Tor is running, changing
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TestingTorNetwork is not allowed.
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9. Start with TestingTorNetwork set and unset it later on which should
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fail.
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tor DataDirectory . ControlPort 9051 TestingTorNetwork 1 DirServer \
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"mydir 127.0.0.1:1234 0000000000000000000000000000000000000000"
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telnet 127.0.0.1 9051
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AUTHENTICATE
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RESETCONF TestingTorNetwork
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513 Unacceptable option value: TestingV3AuthInitialVotingInterval may
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only be changed in testing Tor networks!
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10. Set TestingTorNetwork, but do not provide an alternate DirServer
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which should fail.
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tor DataDirectory . ControlPort 9051 TestingTorNetwork 1
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[warn] Failed to parse/validate config: TestingTorNetwork may only be
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configured in combination with a non-default set of DirServers.
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